Part 1 of sample sprucing.

chrome/test/data/extensions/samples/subscribe/feed_finder.js

+find();
+window.addEventListener("focus", find);
+
+function find() {
+  if (window == top) {
+    // Find all the RSS link elements.
+    var result = document.evaluate(
+        '//link[@rel="alternate"][contains(@type, "rss") or ' +
+        'contains(@type, "atom") or contains(@type, "rdf")]',
+        document, null, 0, null);
+
+    var feeds = [];
+    var item;
+    while (item = result.iterateNext())
+      feeds.push(item.href);
+
+    chromium.extension.connect().postMessage(feeds);
+  }
+}